Embodiments of the present disclosure generally relate to an apparatus for processing substrates. More particularly, the disclosure relates to a batch processing platform for performing atomic layer deposition (ALD) and chemical vapor deposition (CVD) on substrates.
The process of forming semiconductor devices is commonly conducted in substrate processing platforms containing multiple chambers. In some instances, the purpose of a multi-chamber processing platform or cluster tool is to perform two or more processes on a substrate sequentially in a controlled environment. In other instances, however, a multiple chamber processing platform may only perform a single processing step on substrates; the additional chambers are intended to maximize the rate at which substrates are processed by the platform. In the latter case, the process performed on substrates is typically a batch process, wherein a relatively large number of substrates, e.g. 25 or 50 are processed in a given chamber simultaneously. Batch processing is especially beneficial for processes that are too time-consuming to be performed on individual substrates in an economically viable manner, such as for ALD processes and some chemical vapor deposition (CVD) processes.
The semiconductor industry's tolerance for process variability continues to decrease as the size of semiconductor devices shrink. To meet these tighter process controls, the industry has developed a host of new processes which meet the tighter process window requirements, but these processes often take a longer time to complete. For example, ALD is a variant of CVD that demonstrates superior step coverage compared to CVD. ALD is based upon atomic layer epitaxy (ALE) that was originally employed to fabricate electroluminescent displays. ALD employs chemisorption to deposit a saturated monolayer of reactive precursor molecules on a substrate surface. This is achieved by cyclically alternating the pulsing of appropriate reactive precursors into a deposition chamber. Each injection of a reactive precursor is typically separated by an inert gas purge to provide a new atomic layer to previous deposited layers to form a uniform material layer on the surface of a substrate. Cycles of reactive precursor and inert purge gases are repeated to form the material layer to a predetermined thickness. The biggest drawback with ALD techniques is that the deposition rate is much lower than typical CVD techniques by at least an order of magnitude. For example, some ALD processes can use a chamber processing time from about 10 to about 200 minutes to deposit a high quality layer on the surface of the substrate. In choosing such ALD and epitaxy processes for better device performance, the cost to fabricate devices in a conventional single substrate processing chamber would increase due to very low substrate processing throughput. Hence, when implementing such processes, a continuous substrate processing approach is needed to be economically feasible.
New generations of ALD process tools benefit from tight control of the gap between the wafer and the deposition source (injector) to meet composition and thickness uniformity across the wafer and between wafers. The process may take place in a wide range of temperatures, and in a range of separation between the wafer and the deposition source. It can be important to monitor the uniformity of the distance across the wafers area, which can be as large as 1.5 m in diameter. Also, the temperature range that the system works at might be adjusted for thermal expansion to meet the accuracy of wafer placement in the process pockets.
Therefore, there is an ongoing need in the art for apparatus and methods providing control over the injector to susceptor gap over large temperature ranges.